Re: [fuse-devel] Reading from fuse pipe fails with EBADFD

[Nikolaus Rath <Nikolaus@rath.org>]

On Dec 26 2018, Nikolaus Rath <Nikolaus@rath.org> wrote:
>>> >> > When testing FUSE under heavy load, I am occasionally getting EBADFD
>>> >> > errors when reading from the fuse pipe.
>>> >
>>> > EBADFD or EBADF?
>>>
>>> EBADF ("Bad file descriptor"), sorry.
>>
>> Can you run the thing with "strace -f  ..."?
>
> Apologies for the delayed response. I have been trying to reproduce this
> but have instead run into another problem: the *client* getting spurious
> EBADF warnings. I am not sure if this is related or unrelated, and it
> has been hard to debug because it does not happen under strace:
[..]

I believe I have figured it out. I was mistakenly assuming that the bad
file descriptor was the fuse pipe - but it was actually the target file
descriptor (I managed to completely forget that splice works on two file
descriptors).

The root cause was mistakenly closing a file descriptor twice and not
checking the return value. Because of the missing return value check,
the error went unnoticed almost all the time - except when a different
thread managed to re-use the fd for different purposes between the first
and second close.

Apologies for taking everyone's time for what was actually a filesystem
bug.


Best,
-Nikolaus

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